Two decades observing smoke above clouds in the south-eastern Atlantic Ocean: Deep Blue algorithm updates and validation with ORACLES field campaign data

Sayer, A. M.; Hsu, N. Christina; Lee, Jae-Hwa; Kim, Woogyung; Burton, S. P.; Fenn, M. A.; Ferrare, R. A.; Kacenelenbogen, M. S.; LeBlanc, Samuel; Pistone, Kristina; Redemann, J.; Segal-Rozenhaimer, Michal; Shinozuka, Y.; Tsay, Si‐Chee

doi:10.5194/amt-12-3595-2019

Cited by 17 publications

(17 citation statements)

References 116 publications

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“…• direct airborne measurements of the above cloud AOD have shown a slight overestimation by current remote 1165 sensing techniques from space borne instruments (MOD06ACAERO, Deep Blue MODIS and VIIRS) and some potential difficulties in cloud masking (LeBlanc et al, 2020;Sayer et al, 2019), but a generally consistent meridionally distribution between the airborne and orbital observations;…”

Section: Discussionmentioning

confidence: 99%

“…• chemical transport models and climate models exhibit a fairly systematic underestimation of aerosol loadings in the SE Atlantic (Shinozuka et al, 2019;Doherty et al, in prep. ).…”

Section: Discussionmentioning

confidence: 99%

“…Werf, 2010] and as a result, aerosol loading in the ORACLES region was expected to be repeatable, with analyses of 640 MODIS clear-sky AOD retrievals in the project planning stage implying year-to-year variability through the burning season of only 20% of the mean. Since the beginning of the ORACLES project, a number of MODIS and SEVIRIbased retrieval algorithms for above-cloud aerosol optical depth (ACAOD) have been developed [Meyer et al, 2015;Jethva et al, 2018;Peers et al, 2019;Sayer et al, 2019], allowing a study of the interannual variability of the aerosol loading above clouds, which is more relevant for ORACLES science objectives than clear-sky AOD. In this section, 645 we describe the interannual variability of MODIS-detected fire counts, ACAOD, and Sc cloud fractions in August, September, and October for the three ORACLES flights years, i.e., 2016-2018.…”

Section: Aerosol and Cloud Contextmentioning

confidence: 99%

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An overview of the ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) project: aerosol-cloud-radiation interactions in the Southeast Atlantic basin

Redemann¹,

Wood²,

Zuidema³

et al. 2020

Preprint

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Abstract. Southern Africa produces almost a third of the Earth’s biomass burning (BB) aerosol particles, yet the fate of these particles and their influence on regional and global climate is poorly understood. ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) is a five-year NASA EVS-2 (Earth Venture Suborbital-2) investigation with three Intensive Observation Periods designed to study key atmospheric processes that determine the climate impacts of these aerosols. During the Southern Hemisphere winter and spring (June-October), aerosol particles reaching 3–5 km in altitude are transported westward over the South-East Atlantic, where they interact with one of the largest subtropical stratocumulus subtropical stratocumulus (Sc) cloud decks in the world. The representation of these interactions in climate models remains highly uncertain in part due to a scarcity of observational constraints on aerosol and cloud properties, and due to the parameterized treatment of physical processes. Three ORACLES deployments by the NASA P-3 aircraft in September 2016, August 2017 and October 2018 (totaling ~350 science flight hours), augmented by the deployment of the NASA ER-2 aircraft for remote sensing in September 2016 (totaling ~100 science flight hours), were intended to help fill this observational gap. ORACLES focuses on three fundamental science questions centered on the climate effects of African BB aerosols: (a) direct aerosol radiative effects; (b) effects of aerosol absorption on atmospheric circulation and clouds; (c) aerosol-cloud microphysical interactions. This paper summarizes the ORACLES science objectives, describes the project implementation, provides an overview of the flights and measurements in each deployment, and highlights the integrative modeling efforts from cloud to global scales to address science objectives. Significant new findings on the vertical structure of BB aerosol physical and chemical properties, chemical aging, cloud condensation nuclei, rain and precipitation statistics, and aerosol indirect effects are emphasized, but their detailed descriptions are the subject of separate publications. The main purpose of this paper is to familiarize the broader scientific community with the ORACLES project and the data set it produced.

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Section: Discussionmentioning

confidence: 99%

“…• chemical transport models and climate models exhibit a fairly systematic underestimation of aerosol loadings in the SE Atlantic (Shinozuka et al, 2019;Doherty et al, in prep. ).…”

Section: Discussionmentioning

confidence: 99%

Section: Aerosol and Cloud Contextmentioning

confidence: 99%

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An overview of the ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) project: aerosol-cloud-radiation interactions in the Southeast Atlantic basin

Redemann¹,

Wood²,

Zuidema³

et al. 2020

Preprint

Self Cite

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“…where λ is the wavelength. All available (typically four) AOD measurements in the 440-870 nm wavelength range are used in the fit, which is more robust to calibration problems in individual channels than a bispectral approach and accounts for spectral curvature in log(τ λ ) (Eck et al, 1999;Schuster et al, 2006). The uncertainty on mid-visible AOD is dominated by sensor calibration and is ∼ 0.01 (Eck et al, 1999).…”

Section: Background and Methodologymentioning

confidence: 99%

A review and framework for the evaluation of pixel-level uncertainty estimates in satellite aerosol remote sensing

et al. 2020

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Abstract. Recent years have seen the increasing inclusion of per-retrieval prognostic (predictive) uncertainty estimates within satellite aerosol optical depth (AOD) data sets, providing users with quantitative tools to assist in the optimal use of these data. Prognostic estimates contrast with diagnostic (i.e. relative to some external truth) ones, which are typically obtained using sensitivity and/or validation analyses. Up to now, however, the quality of these uncertainty estimates has not been routinely assessed. This study presents a review of existing prognostic and diagnostic approaches for quantifying uncertainty in satellite AOD retrievals, and it presents a general framework to evaluate them based on the expected statistical properties of ensembles of estimated uncertainties and actual retrieval errors. It is hoped that this framework will be adopted as a complement to existing AOD validation exercises; it is not restricted to AOD and can in principle be applied to other quantities for which a reference validation data set is available. This framework is then applied to assess the uncertainties provided by several satellite data sets (seven over land, five over water), which draw on methods from the empirical to sensitivity analyses to formal error propagation, at 12 Aerosol Robotic Network (AERONET) sites. The AERONET sites are divided into those for which it is expected that the techniques will perform well and those for which some complexity about the site may provide a more severe test. Overall, all techniques show some skill in that larger estimated uncertainties are generally associated with larger observed errors, although they are sometimes poorly calibrated (i.e. too small or too large in magnitude). No technique uniformly performs best. For powerful formal uncertainty propagation approaches such as optimal estimation, the results illustrate some of the difficulties in appropriate population of the covariance matrices required by the technique. When the data sets are confronted by a situation strongly counter to the retrieval forward model (e.g. potentially mixed land–water surfaces or aerosol optical properties outside the family of assumptions), some algorithms fail to provide a retrieval, while others do but with a quantitatively unreliable uncertainty estimate. The discussion suggests paths forward for the refinement of these techniques.

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“…Prior studies of the diurnal cycle of marine boundary layer clouds have shown distinct diurnal cycles between stratocumulus and cumulus, with stratocumulus cloud cover attaining a broad-in-time nighttime maximum ending at dawn, attributed to accumulated nighttime radiative cooling (e.g., Rozendaal et al, 1995;Eastman and Warren, 2014;Painemal et al, 2015;Burleyson and Yuter, 2015;Seethala et al, 2018). Surface-forced cumuli clouds, in contrast, produce smaller cloud fractions with a maximum in the late afternoon (Eastman and Warren, 2014) and a minimum at sunrise.…”

Section: Introductionmentioning

confidence: 99%

The diurnal cycle of the smoky marine boundary layer observed during August in the remote southeast Atlantic

Zhang

Zuidema²

2019

Atmos. Chem. Phys.

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Abstract. Ascension Island (8∘ S, 14.5∘ W) is located at the northwestern edge of the south Atlantic stratocumulus deck, with most clouds in August characterized by surface observers as “stratocumulus and cumulus with bases at different levels”, and secondarily as “cumulus of limited vertical extent” and occurring within a typically decoupled boundary layer. Field measurements have previously shown that the highest amounts of sunlight-absorbing smoke occur annually within the marine boundary layer during August. On more smoke-free days, the diurnal cycle in cloudiness includes a nighttime maximum in cloud liquid water path and rain, an afternoon cloud minimum, and a secondary late-afternoon increase in cumulus and rain. The afternoon low-cloud minimum is more pronounced on days with a smokier boundary layer. The cloud liquid water paths are also reduced throughout most of the diurnal cycle when more smoke is present, with the difference from cleaner conditions most pronounced at night. Precipitation is infrequent. An exception is the mid-morning, when the boundary layer deepens and liquid water paths increase. The data support a view that a radiatively enhanced decoupling persisting throughout the night is key to understanding the changes in the cloud diurnal cycle when the boundary layer is smokier. Under these conditions, the nighttime stratiform cloud layer does not always recouple to the sub-cloud layer, and the decoupling maintains more moisture within the sub-cloud layer. After the sun rises, enhanced shortwave absorption in a smokier boundary layer can drive a vertical ascent that momentarily couples the sub-cloud layer to the cloud layer, deepening the boundary layer and ventilating moisture throughout, a process that may also be aided by a shift to smaller droplets. After noon, shortwave absorption within smokier boundary layers again reduces the upper-level stratiform cloud and the sub-cloud relative humidity, discouraging further cumulus development and again strengthening a decoupling that lasts longer into the night. The novel diurnal mechanism provides a new challenge for cloud models to emulate. The lower free troposphere above cloud is more likely to be cooler, when boundary layer smoke is present, and lower free-tropospheric winds are stronger and more northeasterly, with both (meteorological) influences supporting further smoke entrainment into the boundary layer from above.

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Two decades observing smoke above clouds in the south-eastern Atlantic Ocean: Deep Blue algorithm updates and validation with ORACLES field campaign data

Cited by 17 publications

References 116 publications

An overview of the ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) project: aerosol-cloud-radiation interactions in the Southeast Atlantic basin

An overview of the ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) project: aerosol-cloud-radiation interactions in the Southeast Atlantic basin

A review and framework for the evaluation of pixel-level uncertainty estimates in satellite aerosol remote sensing

The diurnal cycle of the smoky marine boundary layer observed during August in the remote southeast Atlantic

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